1. Field of the Invention
The present invention is directed to a method and apparatus, using polarimetry techniques, for the quantitative determination of the concentration of optically-active substances in a carrier, such as glucose in body fluids of a patient.
2. Description of the Prior Art
A known technique for determining the concentration of a substance in a fluid carrier is to generate comparative signal, such as a differential or quotient signal, from respective linearly polarized light beams generated by two light sources. The light beams pass through the fluid to be analyzed, and are incident on a detector. One of the linearly polarized light beams has a direction of polarization which is different from the polarization direction of the other light beam by a predetermined angle. The two light sources are alternatingly switched on and off at a predetermined frequency. The measurement signals produced by the detector, corresponding to the two linearly polarized light beams incident thereon, can be used to generate one or more comparative signals, such as difference or quotient signals. Such a polarimetry method and apparatus are described in German Reference 39 08 114. The method and apparatus disclosed therein permits the identification of the concentration of an optically-active substance in a carrier fluid while reducing the influence of interference, such as from aging of the components which comprise the concentration. This known apparatus and method, however, have the disadvantage of permitting only the acquisition of the sum total of the optical polarizations in the light emerging from the carrier being measured. If other substances are present in the path of the light beam in the carrier, which contribute optical polarizations of their own to the sum total, in addition to the polarization contributed by the optically-active substance whose concentration is to be identified, the concentration derived from the sum total may inaccurately represent the true concentration of the substance in question, due to the presence of the polarizations produced by other substances in the carrier.